Telephone system.



Patented Jan 9, |900 J. R. BLINCK & C. H. WEST.

TELEPHONE SYSTEM.

{Applicationjlet} May 8, 1899.)

5 Sheets-Sheet l..

(No Model.)

.Ne T

me. E, Q

s.. Q .N

INVENTORS fw A7. am

WlTNESSES:

ATTORNEYS Nh. 640,988. y V

- J. n. BLINCK & c. H. WEST .TELEPHONE SYSTEM.

(Application medmay s, 189m' Patented 1an. 9, i900.

(No Model.)

5 Sheets-Sheet 2.,

ATTORN EYS .1. n. BLlNcK & c. H. wEsT. TELEPHONE SYSTEM.

(Application led May 8, 1899.)

(Na Model.)

Patented lan. 9, |900.

5 Sheets-Sheet 3.

No. 640,988". Patented 1an. 9, moo.

1. n. BLlNcK & c. H. wEsT.

TELEPHONE SYSTEM.

(Application filed May 8, 1899.)

(No Model.) 5 Sheets-Sheet '4.

WITNESSES:

TTORNYS Patented lan 9, |900 J. R. BLINCK & C. H. WEST.

TELEPHONE SYSTEM.

(Application filed. May 8` 1899.1

5 Sheets-Sheet 5,

(N0 Model.)

' INVENTQRS ATTORNEYS iliyrrnn j 'STATES tries.

PATENT JOHN R. BLINCK AND CHARLES H. WEST, OF JERSEY CITY, NEV JERSEY.

TELEPHONE SYSTEM.

SPECIFICATION forming part' of LetterSPatent No. 640,988, dated January9, 1906. Application tiled May 8, 1899. Serial No. 715,909. (No model.)

To @ZZ whom t 1710.3/ concern.-

Be it known that we, JOHN R. BLrNcK, a subject of the Queen of theNetherlands, and CHARLES H. WEST, a citizen of the United States, bothresiding in Jersey City, in the county of Hudson and State of NewJersey, have invented an Improvement in Telephone Systems, of which thefollowing is a specification.

Our invention relates to telephone systems, and has special reference tothe class of telephone systems which are nowr designated as party-linetelephone systems-in brief, a system wherein a number of subscribers arecarried upon a single line or plurality of lines, which lines usuallyentera central station or switching-station, the object being to enablethe operator at the central or switching station to call up individualsubscribers on the 2Ol party-line and connect the said subscriber with asubscriber on another or the same party-line and to enable the inactiveinstruments on the said line or lines to be what we herein term locked,which term as used by us herein includes any means of rendei'-,

ing the said instruments ineective tobreak in upon the line.

We will with the aid ofthe accompanying' drawings describe ourinventionand one form or embodiment thereof, it being understood that we do notthereby limit ourselves to the construction and arrangement shown, butrefer to the claims for a succinct statement of the main characteristicsof our invention.

In the accompanying drawings We havev illustrated in Figure l aparty-line entering a central or switching station, which party-line isprovided with a series of instruments or substations, a convenientnumber of which is six, although a less or greater number within limitsmay be connected. In Fig. 2 we have shown the positions assumed by themovable parts of the magnetic 'circuit affected by the magneticcircuit-controllers at the substations when in their ringing, locking,and unlocking positions, as will be fully described hereinafter. In Fig.3 we have shown in detail one form of the circuit arrangement of thesubscribers stations, the same representing the circuit arrangement instations-Nos. l., 2, 3, and et illustrated in Fig. l. In Fig. et we haveshown the 4circuit arrangement of the subscribers station at stations 5and 6 of Fig. l. Fig. 5 shows a detail side view of aportion of thecontroller shown in Fig. 3. Fig. 6 shows an end'ordetail side viewthereof. Fig. 7 is a side view of the reversible key employed at centralin ringing up a subscriber, the said key being arranged to ring up oneparty-line without ringing into the calling-subscribers circuit. Fig. 8is a sectional detail View of the key shown in Fig. '7, the sectionbeing taken on the line 8 8 of Fig. 7. Fig. 9 is a plan View of the key.Fig. 10 is a detail View of the key detached from its support and shownseparately; and Fig. ll is a table of the polarities employed inringing, (from central,) locking, and unlocking.

It is not" deemed expedient to herein describe in detail the principlesupon which the apparatus operates; but in explaining the Various partswe will be careful to state the operations performed and the functionsof the various circuits. y

Referring generally to Fig. l of the drawings, the central or switchingstation (terms herein employed interchangeably) is represented at A, andB, C, D, E, F, and G indicate the substations or subscribers, which willhereinafter be referred to as Nos. l to 6, inclusive, for the purposesof clearer and less redundant description and in accordance with thelogical development of the subject.

It will be observed that the substation-circuits, which will behereinafter fully described with reference to Figs. 3 and 4, areconnected across a pair of lines a b, which will hereinafter be referredto together as the party line or lines. The line a is connected to aline a', which enters the central station and is connected with aspring-jack or plugspring c2. The other line b enters the central orswitching station by the line b', which is connected to a spring b2 ofthe same springjack. The springs a2 b2 cooperate with terminals a4 b",connected to wires a3 b3, connecting with the calling-drop d, which isgrounded through the Wire CZ. A clearing-out drop d2 is likewiseconnected to the ground-wire d by a wire d3. Another pair of party-linese f enter the central or switching station and are connected to theline-springs e f. @2j-"2 are the other pair of springs, which coperatewith the line-springs c f to constitute the calling-jack of the otherparty-line and are connected through wires es f3 with the linedrop g,which is connected by a wire g with the ground-wire d. These connectionsjust described constitute the two jacks employed for answering andcalling, it being understood that one jack is in one party-line or pairof party-lines and the other jack is in another party-line or pair ofparty-lines, the ringing-off drop d2 being common to both plugs.

H I represent, respectively, the answering and calling plugs forcoperating with the answering and calling jacks. These plugs are eachpreferably provided with a pair of contacts h h and t' and fi',respectively. These answering and calling plugs are connected,respectively, with the two sides of the reversible key J. (Shown inFigs. 8 to 10, inclusive.) Fig. l should nowbe read in connection withthe said figures. The contact h of the answering-plug H is connected bya wire h2 with the spring h3 of the reversible key J. The contact h isconnected, by means of the wire h4, with the opposite spring h5. Thesetwo springs h3 h5 cooperate with a pair of springs h6 k7, which areconnected by wires hi h8 to the corresponding springs hw hu of theopposite side of the reversible key.

k12 7tlg are springs which cooperate with the springs h3 h5 and areconnected to the wires h" hw, which are connected with the terminals ofthe calling-off drop d2 and which are adapted to coperate with theterminals 71.14 71,15 of the listening-in key hw, to which the centralor station telephone apparatus K is connected. The wires hw h18 areconnected to springs h1 h2o, which are adapted to coperate with springs7t21h22, which are connected to the contacts tt" of the calling-plug I.The two sides of the reversible key J are employed for the purpose ofenabling the operator to ring into one party-line or the other Withoutringing into the line of the calling subscriber. This reversible key, aswill be obvious from the circuits, may be employed to talk into eitherparty-line independently without talk ing into the other party-line. TheWires hs h9 are connected by the wires a5 b5 to the contact-springs ofan unlocking-key L and to a series of calling-keys la to 6a, inclusive,whose back contacts are connected, respectively, to the lines a6 196,suitable batteries or generators being connected thereto, as indicatedby the polarity-signs on Fig. l. The polarities employed in ringing,locking, and unlocking are as shown in the table of polarities in Fig.11. One spring of each, of the pairsof middle springs in calling-keys la2n 3a 4 is connected to the ground-line G10, so as to ring over agrounded circuit 2, while the middle springs in the calling-keys 5a 6are connected across the calling-lines 0.5 b5 and the outside springs tobattery-Wires a6 b, so as to ring over a metallic circuit. By this meansthe proper connections are made for giving the requisite polarities incalling.

The unlocking-key L needs special description. The line 0,5 is connectedto one of the middle springs t2 of the unlocking-key, and the other lineb5 is connected to the other middle spring Bof the unlocking-key. Theoutside springs t4 are connected together to the negative source b. Theremaining two springs t5 are connected together by the wire t6 and tothe ground-wire G10, and are carried upon insulating-blocks t7, securedto the springs 9, which are both connected to the positive source a6.

By following out the circuits it will be obvious that by depressinganyone of the keys 1a to 6a, respectively, the polarities indicated inthe table of polarities, Fig. 11, may be thrown upon one or both of thelines a b and that the unlockingkey will also give its set ofpolarities, as indicated in the table of polarities. These polaritieswill produce at the substations the effects which will be mentioned indetail when the said substations are described.

The apparatus at the subscribers stations will now be described, and forthis purpose reference should be had more particularly to Figs. 3 and 4.As before stated, in Fig. 3 we have shown in detail the circuitarrangement in subscribers stations Nos. l, 2, 3, and 4, and in Fig. 4the circuit arrangement of subscribers stations Nos. 5 and 6.' Thesecircuit ar rangements differ only slightly, the difference in the wiringbeing necessitated by the fact IOO that the calling or ringing of thesubscriber is effected in stations 1, 2, 3, and 4 over one or the otherof the lines a b used as a grounded circuit, while in stations 5 and 6the calling or ringing is effected over the metallic circuit, as will beobvious from the table of polarities in Fig. 1l. The locking andunlocking are likewise effected by the employment of both sides of theline, as will be obvious from an inspection of the unlocking-key in Fig.1 and from the following description:

Referring for the present particularly to Fig. 3, the telephonicreceiving and transmitting apparatus is connected to line as follows:The wire o, connected to the line-wire a, leads to one side of thereceiver 1', and the wire o' leads to the other terminal of the receiver r, the condenser lo being interposed. These wires to the receiverare adapted to be short-circuited by the swinging armature m of thelocking-relay m through wires o2 03. The station-transmitter t isconnected into the primary circuit of the induction-coil T through wirest', station-battery S B, wire t2, telephone-switch s, and wires t3 t4.The magnetic circuit-controlling magnet or controller p, by which thecall or ringing is effected in the subscribers station, is connected tothe line ct through the wire 04 and to the line b by the wire o5, themiddle point of the Winding of the controller being connected to theground G (or the ground G5 in Fig. 4) by the wire 06. The action of thecontroller p is to modify the effect of the permanent-magnet IIO yoke nupon the pivoted bars n n2, which are pivoted to the terminals n3 n4 ina manner well understood.

Referring for the moment to Fig. G, it will be noticed that the pivotedbar n carries a small leaf-spring n, Which makes a rubbing contact withthe pole a6 of the permanent magnet n. The bars n n2 swing freely in thespace between the poles of the electromagnet of the controller and thepole-pieces of` the yoke nl of the controller, as will be clearly seenby an inspection of Fig. 5, so that the action of thecontroller-electromagnets is to modify the effect of thepermanent-magnet yoke n to produce the swing of the bars, and it is bysuitable combinations of polarities transmitted from the central stationor switching station that the bars may be thrown into suitable positionsto effect the ringing and unlocking of the subscribers stations, and, aswill be presently explained, the locking taking place through the actionof a subscriber ringing central.

A diagram of the positions assumed by the armatures of thc variousstations in ringing, locking, and unlocking is exhibited in Fig. 2, inwhich no to x0 represent the positions of the armatures in the stations1, 2, 3, 4, 5, andt, and y' to y the positions of the armatures inlocking at the various stations, and z to ,c6 the positions ofthearmatures in unlocking at the various stations. A bell or othersignal-receiving device q is located at the subscribers station. When asubscriber is called, this bell is rung by the action of the bars n n2,or one of them, closing the circuit of the bell. The bell-circuits areas follows: As it will be understood, the ringing of the .bell iseffected by the station-battery S B. From the oppo- `site poles of thisbattery two wires o7 o8 lead to the terminals n3 n4, respectively, towhich i the bars n' n2 are pivoted. An` additional wire o40 leads fromthe wire o9 of the bell to the front contact 050 of the bar n. The barnl, as before stated, is provided with a spring '17.5, which makesrubbing contact with the permanent-magnet yoke n, to which yoke'one ofthe terminals of the bell q is connected by the wire oi. The otherterminal of the bell is connected by the wire o10 with the back contacto, with which the bar n2 cooperates, so that the passage of a current ofsuitable polarity, let us say, over the line b to ground will cause thebar n2 to strike against the contact ou, as indicated at zr in Fig. 2and in the table of polarities, Fig. 11, thereby closing thebell-circuit and causing the same to ring. A wire o2b leads from thewire 010 to the spring Z of the calling-generator switch for a reasonpresently to be explained. The locking-relay m is connected in circuitin the following manner: One of its terminals m2 is connected by wireo12 to the wire 013, which runs to the back contact 027, which coperateswith the bar n. The wire o13 likewise connects with the wire 014, whichis connected to the front contact 015 of the bar n.2. The wire o13 iwires 021022. generator, itscircuits, and connection with the continuesonward and is connected to the spring o16, which receives the impact ofthe spring Z of the substation ringing-generator Z, as willbe explained.It must be understood that this generator is not necessarily amechanically-operated device, but may be batteries, &c. The oppositeterminal m3 of the locking-relay is connected by the wire o17 with theWire 018, connected to the contact Z2 ofthe rin ging-generator and tothe terminal s' ofthe short-circuiting telephone-switch, the terminal s2of the short-circuitin g telephone-switch being connected bythe wire 02to the wire 012, running to the terminal m2 of the locking-relay, sothat when the telephone-hook is up the locking-relay will beshort-circuited- The function of the lockingrelay is to short-circuitthe telephone transmitting and receiving apparatus and the rin ging-generator Z, so that when the armature m of the said locking-relay isset by an impulse or impulses into the positions shown in Figs. 3 and tthe' armature m of the said locking-relay will short-circuit thetelephone apparatus through the wires 02, o3 and will'short-circuit thegenerator l through The construction of the cal1inglines will now bedescribed. This generator is herein shown as amechanically-operatedcontinuous-current generator Z, one terminal of which is groundedthrough the wire'ZS and the other terminal of which is connected,through the wire Z4, to a contact liwhich is adapted IOO to`coperatewith a line-spring o23, which is A connected, through wire 024,to the line a and -whichis adapted to coperate with another line springor wire c25, which is connected to the line Z). The subscriber turnsthecrank Z10 of the rin gingegenerator Z, Vthereby swinging the pivotedlevers Z6 bythe wheel Z7 and pin-aud-slot connection Z8, so as to causethe. end Z9 of the lever Z6 to bring the spring 02.5`

against the spring 023 and the latter against the contact or terminalZ5, so as to call central through `both sides of the line andtheground-wire Z3, it being remembered that the calli'ngdrop d atthecentral (see Fig. l) is connected to both sides of the line throughthe wires Ct Z9' and` grounded through the ground-.wire CZ'. At the sametime the spring IIO IIS

Z is carried away from contact Z2 and brought into contact with spring016, thereby completing the bell q circuit locally and opening thecircuit of the locking-relay, thereby blocking the samey to prevent itfrom being operated by the unlocking apparatus at central.

The construction shown in Fig. 4t is quite vsimilar to that shown inFig. 3, with the exception that the connections of the contacts of thebars n n2 are` arranged slightly differently, as the calling or ringingis effected' from central by the employment of a metallic circuitinstead of a grounded circuit, as in Fig. 3, the ground-circuit throughthe middle of the controller-magnet being preserved for the purpose oflocking and unlocking the instruments. A reference to Fig. 1l of thetable 0f 150ml-ities win disclose the fact that both unlocking andlocking are effected over a grounded circuit.

In Fig. 4,which, as before stated, illustrates the organization of thestation-circuits at substations 5 and 6, the contact o50 is connected tothe wire 012 by the wire 028 instead of being connected directly to thebell-terminal by-wire 040, as in Fig. 3. The bell is sprung acrossbetween the wire 010 and the contact o27 through wires 029 and 020.

It now remains to describe the construction of the reversible key J. Forthis purpose reference is to be had to Figs. 7 to l0, inclusive. Inthese figures the key J is shown as pivoted by a shaftj in a bearingj12.The key .l is provided with a plurality of oppositely-placed camsj2j3,which act upon plungers 3'47'5 to depress either one or the other,accordingly as the key is swung to one side or the other to engage oneor the other of its cams with the appropriate plunger.

TheA detailed operation of the sytem is as follows: We will describe acomplete operation whereby the central is called up, and a connectionbetween the station shown in Fig. 3 of the drawings is effected with thestation shown in Fig. 4 of the drawings by means of the central. 3 willbe designated Station l, andthe station represented in Fig. 4 will bedesignated Station 5. The party at station 1, seizing the handle ZIO,sets the generator in action, brings the contact-springs o23 o25together, separates Z from Z2, and brings Zi in contact with spring 016.As one side of the callinggenerator is grounded at Z2, the currentpasses through wire Z4 to Z5 and thence through 023 o24 025 to the linesa and Z). Part of the current traverses the lines c Z) to the centralstation, where it operates the calling-drop OZ. Part of the currentlikewise passes through wire, 04 and through a spool of one of thecontrollermagnets to the ground at o, and another part 'of the currentpasses by wire o5 through the spool of the other controller-magnet tothe ground at 06. These currents will actuate the bars n n2, so thatthey will assume the position shown at y in Fig. 2, it being linderstoodthat calling the central station will effect the locking of the otherinstruments on the line. If 1j of Fig. 2 be kept in mind, the circuitsin Fig. 3 may be traced as follows: from the positive pole of thestation-battery S B by wire o7 to n3, thence by n to 050, thence by 040tothe bell-terminal, through the bell, thence by wire o2G to the springZ', which is in contact with spring o16, through which the currentpasses to wire 012, thence by wire o14 to the back contact 015 of thebar n2, and thence by wire o8 to the negative pole of the battery. Itwill be observed that this current will ring the bell q-that is to say,the calling-subscriber rings his own bell, as well as throws the drop atthe central. lle does not, however, actuate his own locking-relay, forthe said locking-relay, although it is connected The station representedin Fig.`

eadess to wire 012, has its circuit broken at Z and Z2. lt willconsequently remain inactive; but it is to be noted, however, that inringing the relay is not in the position shown in Figs. 3 or 4, but inan intermediate position. The relay is shown in Figs. 3 and 4 in itsshort-circuiting position for the purposes of clearer illustration.

Having observed the effect of the callingcurrent at the subscribersstation, let us pass to the other stations on the line, using thestation shown in Fig. 4 as an example. This station being the fifthstation on the line, we turn to Fig. 2 and observe the position assumedby the bars at if inorder to aid us in tracing the circuit. The currentsenter through lines a b by wires o4 and o5, actuate thecontroller-magnets, and go to ground at G5, thus throwing the armaturesinto the position shown at if in Fig. 2. Commencing at the positive poleof the battery, the circuit may be traced as follows: by wire o7 to 723,thence by n to 052, thence by 02s to 012, through 012 to m2, through thelocking-relay by wires 017 018 to Z2; thence by Z, wire 026, backcontact o, bar H2124, and wire oS to the negative pole of the battery.It will be observed that the current in this instance does not passthrough the bell q, but actuates the lockingrelay to throw it into theposition shown inV Fig. 4, so as to lock this station. The saine thinghappens at. all the other stations on the` l' line except thecalling-station, as the relaycircuit at this station is openat Z2.Station No. l now asks the central to connect him with No. 5. Thereuponthe central throws down her unlocking-key and unlocks the entire line.The unlockingcircuits will be traced in Fig. 3. Turning to'Fig. 2, at cwe get the positions ofthe bars a n2 as the central sends a negativecurrent over both sides of the line to unlock. Starting from thepositive pole of the battery, the current passes by wire o7, bracketn.3, bar n', wire 012, wire 012, locking-relay m, wires 017 018, contactZ2, spring Z', 'wire 026, wire 010, bar n2, and wire o8 to thenegativerpole of the battery. In Fig. 4 the same unlocking-currentpasses, the movable bars being in the positions z5 in Fig. 2. The localunlocking-circuit is as follows: by wire 07, bracket n3, movable bar n',wire 030, bell q, wires o29 026, spring Z, contact Z2, wire 018, wire017, locking-relay mi, wire 012, wire 013, wire 014, bar n2, and wire o8to the negative pole of the station-battery. This is effective to unlockthe station; but it is to be observed that the bell q does not ring, forthe reason that by the position assumed by the movable bars at n2 it isin series with the locking-relay m, and as the locking-relay has aresistance of some forty or fifty ohms and the bell a resistance of butin the neighborhood of five ohms the locking-relay alone will beactuated. Having unlocked the line, the central now proceeds to call upthe station shown in Fig. 4. This she does by sending a negative currentover line a and a positive current over line ZJ, the

IOS

IIO

ground being neutral. This has the effect of throwing the movable barsn' n2 into the positions'shown at x5 in Fig. 2. The local circuit willthen be as follows: by wire 07, bracket n3, bar n', contact o, wire 030,bell q, wire 029, wire 010, bar n2, and wire o8 to the ative pole of thebattery. The parties thus connected may converse immediately, or, itthey desire, either may by use of the ringinggenerator lock out all theother instruments on the line except the two who are talking, theirrelays being now short-circuited th rough the receiver-telephone hook.When the two on the same party-line have finished their conversation,either may ring off with his ringing-generator, the signal beingreceived on the clearing-out drop d2 at the switchingstat-ion, whereuponthe operator at the central or switching station depresses theunlocking-switch to unlock the line and restore the apparatus to itsnormal condition.

Having described our invention, what we claim, and desire to secure byLetters Patent,

l. In aselective signaling system, the combination of substationslocated along a double-conductor main line, a magnetic circuit locatedlat each substation and having a plurality of independently-movableelements, a local signaling device at each substation ina circuitresponsive to a change in the position of a movable part or parts of themagnetic circuit and electromagnets each responsive to a current sentover one side of the line and governing the action of one of the saidmovable elements, and a central or switching station provided withsignaling means sending particular currents or current combinations forselectively signaling the substations.

2. In a selective signaling system, the combination of a series ofsubstations and a central station, a metallic or double-conductor maincircuit, a ground connection at each substation normally in circuit withboth sides of the line and means under the control of the subscriber ateach substation for transmitting current over both sides of the circuit,locking or short-circuiting means at each substation responsive theretoand means for preventing the locking or short-circuiting means at thestations in use for talking, from being operated by such current.

3. In a signaling system of the character described, the combination ot'a series ofsubstations in electrical connection, with a double-conductormain line or circuit, a groundcircuit at each substation normallyconnected to both sides of the line, means at each substation forsignaling the same from the switching-station by a particular current orcurrent -combination for each substation, means located at eachsubstation for locking or shortcircuiting the other subscribers stationsand means at each substation under the control of the subscriber forrendering the locking or short-circuiting device ot his stationinoperative when a call is desired to be sent to the central whereby hisown instrument will not be locked out when he signals central.

4. In a signaling system of the character described, the combination ofaseries of substations in electrical connection with both sides of adouble-conductor main line or circuit with selective signaling apparatussubstantially as described located at the central and substations; aground circuit permanently connected to both sides of the line, alocking-relay located ateach substatiomand circuit connections with thesaid locking-relaycombined with means for manipulating the circuit ofthe said locking-relay by the transmission of a call from a substationto central to render the said locking-relay inoperative to lock thecalling-subscribers substation.

5. The combination, in a signaling system, of a series of substations inelectrical connection with a double-conductor main circuit withselective signaling apparatus substantially as described located at thecentral and sub stations, a locking-relay located at each substation, acalling-generator at each substation and movable means for automaticallyconnecting the calling-generator with both sides of the line and foralso opening the circuit ot the locking-relay at the substation wherethe calling-,generator is operated.

6. An electrical signaling system compris' ing a metallic ordouble-conductor main line or circuit extending between a central orswitching station and a number of substations, a signal-receiving devicein a local circuit at each substation, a normally-magnetized loop oryoke of magnetic material constituting a magnetic circuit and aplurality of electromagnetic means connected one to each side ot theline at the substation separate and distinct from the said magneticcircuit and adapted to control the same, means for thereby actuating thesignal-receiving device, an earth conductor normally in circuit withboth sides of the line and a series of signal-transmitting devices at .acentral or switching station for sending currents to effect the properchange in the devices for manipulating the magnetic circuit at therespective substations so that the receiving device of the substationrepresented by such signal device and no other is responsive,substantially as described.

7. In a selective signaling system, the com bination of a series ofsubstations having individual locking apparatuses and a central station,means at each substation for operating the locking apparatus of theother stations on the line, means at the central station for unlockingthe line and means at each substation for blocking its locking apparatuswhen a call has been sent from-that substation so that the unlockingapparatus at the central station is inoperative to operate the lockingapparatus at the said substation.

8. In a signaling system of the character described, the combination ofa series of subrecf IIO

stations in electrical connection with a doubleconductor main circuit,and having individual locking apparatus, means at each substation forreceiving signals from the switching-station by particular current orcurrent combinations for the substations, means at each substation foroperating the locking apparatus of the other stations on the line, meansat the central station for unlocking the line and means at eachsubstation for blocking its locking apparatus when a call has been sentfrom that substation so that the unlocking apparatus at the centralstation is inoperative to operate the locking apparatus at the saidsubstation.

9. In a selective signaling system, the combination of a series ofsubstations having in- JOHN R. BLINOK. CHARLES H. WEST.

Witnesses:

GEO. E. MORSE, CHARLES E. SMITH.

of the other stationspart of the locking z5

